Which type of specimen has a recommended storage time of 42 days following transfusion?

A blood sample is the correct answer because it is crucial for the safe and effective use of blood transfusions. Following a transfusion, blood components, particularly red blood cells, should be properly stored and monitored to ensure their viability and safety for recipients. The recommended storage time of 42 days allows for blood to be maintained at proper conditions, preventing spoilage and ensuring that the transfused product retains its necessary properties for patient care.

In contrast, urine samples, stool samples, and sputum samples have different guidelines for storage and use. For example, urine and stool samples are typically processed within a much shorter time frame due to their susceptibility to degradation and changes in composition, which can affect test results. Sputum samples also have a limited storage duration, primarily because they can become contaminated and lose their diagnostic relevance. Thus, the 42-day storage recommendation applies specifically to blood specimens in the context of transfusions.